The commonly accepted paradigm of WNV is that it is maintained in a bird mosquito bird cycle with transmission to human and other mammalian species by bridge vectors. The role of mammals in the ecology of WNV has not been well defined. Recent evidence suggests that cottontail rabbits might play a role in the ecology of WNV because WNV serum titers can exceed 10 5.5 CID50s/ml which is sufficient to infect potential enzootic bridge vectors. This information is important because cottontail rabbits are peridomestic and could be a source of WNV for peridomestic anthropophilic mosquito species. Other peridomestic mammals such as rats, deer mice, squirrels, raccoons and deer might also be sources of virus "or mosquitoes. The present proposal addresses this possibility by determining the vector competency of Aedes vexans and Ochlerotatus triseriatus with respect to the levels of viremia that occur both in avian and different mammalian species. Both species are common in the upper Midwest and are highly anthropophilic. Accordingly the extrinsic incubation period, susceptibility to WNV infection by the range of virus doses that occur in viremic vertebrate hosts, the transmission rates associated with these infective virus doses, the effect of WNV infection on longevity and spontaneous flight activity will be determined. The ability of both mosquito species to transmit the virus transovarially will also be determined. Concurrently the duration and magnitude of WNV viremias in peridomestic mammals will be characterized. The sero-prevalence of WNV antibody in wild populations of these animals and the frequency by which different mosquito species use them as hosts in WNV active sites will also be determined. Collectively the information acquired in this study will provide a better understanding of the ecology of WNV and lead to the development of improved surveillance and control measures.